Introduction

Query Attributes are a relatively new feature of the MySQL Protocol. This is availble since MySQL 8.0.23.

Before Query Attributes were introduced there already was already another similar feature: Connetion Attributes, which provides per-connection metadata in the form of key/value pairs.

This is what connection attributes look like:

mysql> SELECT ATTR_NAME, ATTR_VALUE
    -> FROM performance_schema.session_connect_attrs
    -> WHERE PROCESSLIST_ID=64;

Tweet

Query attributes have in a long time been used to add metadata to queries to provide additional context such as where in the application the query was generated. The traditional way to do this is to add a comment at the start of the query with the attributes. Since the MySQL parser ignores the comment, it does not change the semantics of the query, but various tools can extract the comments.

This post looks into the reasons for using query attributes, how it is done using a comment, and the new component for MySQL 8.0.23 that provides native support for query attributes.

Advice

Query attributes are also known as query tags.

Why Query Attributes?

At the surface, it may seem that there is no major benefit from having metadata …